The present invention relates to tables or beds for supporting substrates being printed upon, and more particularly, to stationary or movable beds or tables used in graphic printing machines incorporating a vacuum to hold an article being printed upon in place.
Assignee of the present invention, MandR Printing Equipment, Inc., Glen Ellyn, Ill., makes several successful printing presses, such as the PROCESSOR(copyright), the RENEGADE(trademark), the LONG STROKE(trademark), the PATRIOT(copyright), the ECLIPSE(trademark), the SATURN(trademark), and the CONQUEST(trademark) screen printing systems. In such systems an article to be printed upon, usually paper or film, is placed upon a bed or table and the table is either stationary or moved through stations where colors are applied to the article. Each color is applied separately through screen printing. At times during the printing process the article is also cured or dried through conventional and well known means to set the ink and prevent smearing etc. It is critical to maintain the article to the bed or table in a set position to ensure consistent and accurate indexing or registration. In short, the article must not move while it is in the system and being worked upon. Any movement will cause misalignment of the images printed upon.
To accomplish this, the article is fixed to the bed by vacuum forces. The vacuum created holds the article/substrate to the table and in a fixed, set position. The substrate is first laid or placed on the table""s top surface and next positioned and oriented on the table. The vacuum is turned on and the substrate is held in place. The table or bed then progresses through the printing machine and is printed upon. Thus, while the table is moved to printing or curing stations and/or acted upon by the printing or curing operation, the article/substrate does not move relative to the table/bed.
The vacuum is achieved by having the bed/table communicating with a vacuum blower and small vacuum holes in the upper surface of the table/bed, namely the surface contacting the article. The vacuum within the bed causes suction from the small openings, pulling the substrate to the table and holding the substrate in the fixed position.
The beds can be very large planar surfaces (e.g., 156xe2x80x3 (vertical) by 72xe2x80x3 (horizontal)). They can hold sheets of many different sizes. The zone of vacuum from the bed is generally the entire upper surface. As such, the entire bed is drawing a vacuum if the sheet is large or if the sheet is small. There is presently no way of controlling this vacuum zone, e.g., applying the vacuum only to the area of need or the size of the sheet. If a sheet is only an eighth of the size of the table, seven-eighths of the table will unnecessarily be drawing air with nothing to hold down. This diminishes the vacuum and reduces the hold-down abilities of the system. Indeed, to maintain a proper vacuum to hold a sheet on a table, the vacuum zone (the area on the table where a vacuum is present from the table acting upon the sheet resting upon the table) should correspond directly to the exact location, orientation, size and shape of the sheet.
Consequently, to optimize the vacuum created on the article, the portion of the bed not covered by the article is masked, meaning the small vacuum holes are covered with tape. In actuality, a worker or operator masks off the top surface with tape in those areas void of the substrate or sheet. This is very time consuming and can take hours for each project. Thus, if the sheet being printed upon is only a third the size of the bed, two-thirds of the bed is masked by hand. This translates to lost production time, wasted materials [tape] and increased expenses.
As a result, there is a need to control the size and location of the zone of the vacuum on the surface of the bed/table so that articles and substrates of different sizes can be easily accommodated.
The present invention discloses techniques and systems for controlling the vacuum area on the bed. The vacuum zone can be adjusted and maintained within minutes as opposed to hours. It can easily be changed from print job to print job and can be replicated for similar jobs. An operator can adjust the location and size of the area on the bed to draw the vacuum. Five embodiments and techniques are disclosed herein.
According to an aspect of the present invention, a vacuum table or bed for holding an article or substrate, such as paper, on the top thereof is disclosed. The table includes a table body having a vacuum source connected to it. The table has a plurality of air holes in the top which define a vacuum zone. This vacuum zone is the zone of xe2x80x9csuctionxe2x80x9d caused by drawing air through the holes in the table by the vacuum connected to the table. The size of this zone is adjustable to accommodate articles having different widths and heights. Specifically, the table has a top sheet having a plurality of holes spaced apart therein and a bottom sheet spaced apart from and below the top sheet. The vacuum chamber is formed between the bottom sheet and the top sheet. The vacuum source, commonly a vacuum blower, is in communications with this vacuum chamber such that surrounding air is drawn through the holes in the top sheet. This aggregate or collection of holes in the top sheet drawing air define the vacuum zone to hold the substrate on the top sheet and to the top sheet. The vacuum chamber acts as a large valve or control center for directing air and vacuum between the vacuum source and the top sheet. In its simplest form, this chamber turns off certain portions of the chamber and turns on other portions of the chamber. In those xe2x80x9conxe2x80x9d areas in the chamber, a vacuum is formed in the top sheet generally directly above this portion of the chamber [the vacuum zone]. In the xe2x80x9coffxe2x80x9d portions of the chamber, air does not flow and no vacuum is formed in the top sheet.
A separation sheet with perforations therein is disposed between the top sheet and the bottom sheet and above the vacuum chamber. A honeycomb support structure with openings therein is disposed between the top sheet and the bottom sheet and above the separation sheet. Thus, air drawn through the holes in the top sheet pass through the openings in the honeycomb support structure and through the perforations in the separation sheet to the vacuum chamber.
Several techniques are shown to adjust both the width and the height of the vacuum zone. In some of the embodiments the position of this vacuum zone is also adjustable. This allows one to control and adjust the size of the vacuum zone created on the top sheet to hold substrates of different sizes. In a first embodiment the means within the vacuum chamber for controlling and adjusting both the height and the width of the vacuum zone includes a plurality of L-shaped channels in communications with a primary vacuum tube. Two pistons are moveable within this primary vacuum tube to block air from being drawn through select L-shaped channels. The pistons are interconnected to one another by a screw such that they simultaneously move towards one another or away from one another. By moving the pistons, air is blocked from selected channels. The blocked channels do not draw any air through the holes in the top sheet above the blocked channels. Thus, by increasing the number of channels blocked, the size of the vacuum zone is reduced. Because of the L-shape of the channels and their alternating configuration (right faced channel, left faced channel, right face channel) both the horizontal and vertical size of the vacuum zone are affected by moving the pistons.
In a second embodiment the means within the vacuum chamber to control and adjust the size of the vacuum zone includes a plurality of vertical gates or stip valves with apertures therein and horizontal gates or strip valves with apertures therein. Each gate is movable between an open position, wherein the air can flow between the vacuum chamber and the top sheet, and a closed position, wherein the air is prevented from flowing between the vacuum chamber and the top sheet. Each gate is a substantially flat stip with a plurality of collinear apertures therein. The vertical gates are parallel to one another and the horizontal gates are parallel to one another. The vertical gates are substantially perpendicular to the horizontal gates. In the open position the apertures in the gate are aligned with the perforations in the separation sheet adjacent the gate and the holes in the top sheet. Each gate can be independently set to open or closed; thus, both the location and the size of the vacuum zone can be set. When two gates are open, the air is free to flow between the top sheet and vacuum chamber. A vacuum is thus generated on the top sheet just above the open gates. By closing one gate, air is blocked between the vacuum chamber and the holes in the top sheet directly above the closed gate. In short, the blocked area does not draw any air through the holes in the top sheet directly above it. Thus, by increasing the number of closed gates, the vacuum zone is reduced. Because the gates are oriented along two axis, both the horizontal and vertical size of the vacuum zone can be affected by opening/closing gates.
In a third embodiment the means within the vacuum chamber to adjust the size of the vacuum zone includes a means for controlling and adjusting the width of the vacuum zone and a separate means for controlling and adjusting the height of the vacuum zone. The means for controlling and adjusting the height of the vacuum zone includes a plurality of horizontal channels in communications with a vertical primary vacuum tube. Like the first embodiment, two pistons are moveable within the primary vacuum tube to block air from being drawn through select channels. However, in this embodiment, the pistons are independent of one another. The means for controlling and adjusting the width of the vacuum zone includes a plurality of blocks, one block in each channel, that are movable within the channels. The blocks are interconnected to one another such that by moving one block, other blocks move with that one block. The blocks are connected to one another by cables entrained around pulleys.
Thus, four control handles adjacent the bed control the location and the size of the vacuum zone; two handles control the position of the pistons with each handle connected to a piston and two handles control the blocks with each handle connected to approximately half the blocks. Again, by moving the pistons, air is blocked from selected horizontal channels. The blocked channels do not draw any air through the holes in the top sheet above the blocked channels. By increasing the number of channels blocked, the vacuum zone is reduced. This blocking controls the size of the vacuum zone in one direction. The blocks within the channels control the size of the vacuum zone in the other direction. Specifically, the blocks within the channels can be moved towards the primary vacuum tube which will reduce the size of the vacuum zone by blocking air flow in part of the channels.
In the fourth embodiment, the means within the vacuum chamber to adjust the size of the vacuum zone includes both a means for controlling and adjusting the width of the vacuum zone and a separate means for controlling and adjusting the height of the vacuum zone. The means for controlling and adjusting the height of the vacuum zone includes a plurality of horizontal channels in communications with a vertical primary vacuum tube. At least two pistons moveable within the primary vacuum tube are provided to block air from being drawn through select channels. The means for controlling and adjusting the width of the vacuum zone includes a plurality of parallel gates transversing the parallel channels. Each gate is movable between an open position and a closed position. In the open position, air flowing in the channel can pass through the gate and eventually between the vacuum chamber and the top sheet in that portion of the unblocked channel. In the closed position, air is prevented from flowing through the gate, blocking off a portion of the channel and preventing air from flowing above that blocked portion of the channel to the top sheet.
Each gate is a hollow sleeve with opposed openings therein and a core slidably positioned within the sleeve having passageways therein. In the open position the passageways within the core are aligned with the openings in the sleeve. In the closed position the passageways within the core are not aligned with the openings in the sleeve. Each gate can be independently set to open or closed, thus controlling the size of the vacuum zone. As before, by moving the pistons, air is blocked from selected channels. The blocked channels do not draw any air through the holes in the top sheet above the blocked channels. Thus, by increasing the number of channels blocked, the vacuum zone is reduced. By moving the blocks, portions of the channels are blocked off and air is blocked from that portion of the channel. A vacuum is thus not created in the area on the top sheet where the channels below the top sheet are blocked.
In the fifth embodiment the means within the vacuum chamber to control and adjust the size of the vacuum zone includes a hose positioned within the vacuum chamber that can inflated and deflated. A plurality of handles adjacent the bed are provided for positioning the horizontal and vertical boundaries or borders of the hose. The handles are maneuvered to put the deflated hose in a desired location. The hose thus forms a xe2x80x9cclosedxe2x80x9d boundary (e.g., a polygon, such as a square or rectangle, or a circle). The hose is inflated and seals the vacuum chamber by its expansion. The area within the boundaries of the hose are in communication with the vacuum source. Thus the vacuum zone is formed on the top sheet in the area above the inflated hose within the boundaries of the hose. Those areas outside the boundaries of the hose do not draw air through the top sheet and thus not under a vacuum.
Other features and advantages of the invention will be apparent from the following specification taken in conjunction with the following drawings.